This application claims priority under 35 USC xc2xa7119 of application number TO2000A 001001, filed Oct. 23, 2000 in Italy.
The present invention relates to a method of positioning turbine stage arrays, particularly for aircraft engines.
As is known, an aircraft engine comprises a multistage compressor; a combustor; and an axial multistage expansion turbine, each stage of which comprises a stator fixed angularly about an axis of the engine, and a rotor rotating about the axis.
As known from European Patent EP0756667, to maximize the aerodynamic efficiency of the turbine, the stators all have the same number of blades and, considering a first and a second stator forming part of two consecutive stages in the axial flow direction of the gas in the engine, the angular position of the second stator about the engine axis is set with respect to that of the first stator as a function of the paths of the wakes generated by the first stator and flowing into the rotor interposed between the first and second stator.
More specifically, the second stator is positioned to roughly align the leading edges of the second-stator blades with the wakes from the rotor.
The above known positioning method is not always satisfactory and at times may either have no effect at all or even the opposite effect, i.e. tests show a reduction as opposed to an increase in the aerodynamic efficiency of the turbine as compared with that obtainable with the stator set to any angular position.
It is an object of the present invention to provide a method of positioning turbine stage arrays, particularly for aircraft engines, designed to provide a straightforward systematic solution to the above problem.
According to the present invention, there is provided a method of positioning arrays of stages of a turbine, particularly for aircraft engines, the turbine having an axis and comprising a first, a second and a third array arranged consecutively and comprising a number of first, second and third blades respectively; said first and said third array having a relative velocity about said axis with respect to said second array; the method comprising the step of determining the paths of wakes moving inside gaps defined by said number of second blades and towards said third array, and the step of regulating the position of said third array with respect to said first array as a function of said wakes; and being characterized by also comprising the steps of distinguishing, for each said wake, a first and at least one second zone differing from each other, and of selecting one of said first and said second zone; the position of said third array being regulated by aligning the leading edges of said number of third blades with the paths of the selected wake zones.